Chitin is an aminopolysuccharide present in exoskeletons of Crustacea, Insecta and the like, in which a repeating unit has one acetylamino group. It is reported that chitin has interesting properties such as high adsorptivity to biological substance, metal and so on, and also wound healing effect.
For utilizing the above mentioned property of chitin, some of porous chitin shaped articles have been proposed in printed documents. However, they did not serve in actual use because of lack of mechanical strength. For example, U.S. Pat. No. 3,988,411 (column 8, line 48) discloses chitin shaped articles including sponge, but it does not disclose concretely the preparation thereof. The use of chitin sponge is also disclosed in "Proceedings of the First chitin/chitosan Conference", National Technical Information Service, U.S. Department of Commerce, Springfield, V.A.22161, (1977), pages 296-305, an article "Application of chitin and chitosan in wound healing acceleration". In the above article, page 300, lines 16-24, it is disclosed that a chitin sponge is prepared by mixing sodium sulfate with a chitin solution formed from a similar process with a cellulose viscose one and then eluting sodium sulfate therefrom. However, there is no description relating to mechanical properties of the chitin sponge.
The inventors of the present invention attempted to apply known processes for a porous cellulose article to the preparation of a chitin article. Examples of known processes include a process which comprises vigorously mixing a viscose solution with a homomixer and then coagulation, and a process which comprises adding a foaming agent to a viscose solution and then foaming it by way of acid or heat, before or during coagulation, to obtain a porous article. It is also known that a process comprises adding a water-soluble compound other than sodium sulfate mentioned above, such as sodium chloride, sodium phosphate and the like, to a viscose solution, coagulation and then removing the water-soluble compound therefrom. In the above attempt by the inventors, the viscose solution was substituted by a chitin solution obtained from a similar process with the viscose one or from dissolving chitin in a solvent. The attempt has failed, because the resultant articles did not have sufficient porosity and were not strong enough to use, especially in wet condition.